The ability to easily and rapidly measure dopamine (DA) release in awake, freely moving animals would be an important research tool. This proposal will utilize IN VIVO ELECTROCHEMICAL DETECTION, a relatively new technique to measure striatal DA release in unanesthetized, unrestrained animals. Two aspects of the effects of incomplete lesions (6-hydroxydopamine method) of DA neurons on striatal DA output will be studied: 1) the effects of graded DA neuronal loss on DA release from surviving nigrostriatal neurons, and 2) the ability of two drugs of potential benefit for the treatment of DA deficiency states (tyrosine and tetrahydrobiopterin) to increase striatal DA release. The lesioned and unlesioned striata will be simultaneously monitored allowing each animal to serve as its own control. The results will aid in understanding and possibly treating a variety of neuropsychiatric conditions with altered DA function including Parkinson's disease, tardive dyskineas, and psychotic disorders.